In this study, we measured transfection efficiency in vitro and in vivo using the following nonviral approaches of gene delivery: injection of plasmid DNA, electroporation -assisted, liposome -enhanced, and integrin -targeted gene delivery, as well as the combination of these methods. Four histologically different tumor models were transfected with a plasmid encoding the green fluorescent protein ( GFP ) ( B16 mouse melanoma, P22 rat carcinosarcoma, SaF mouse sarcoma, and T24 human bladder carcinoma ) using adherent cells, dense cell suspensions, and solid tumors. Emphasis was placed on different electroporation conditions to optimise the duration and amplitude of the electric pulses, as well as on different DNA concentrations for effective gene delivery. In addition, transfection efficiency was correlated with cell density of the tumors. The major in vivo findings were: ( a ) electroporationassisted gene delivery with plasmid DNA, employing long electric pulses with low amplitude, yielded significantly better GFP expression than short electric pulses with high amplitude; ( b ) electroporation combined with liposome -DNA complexes yielded the highest percentage of transfected tumor area in B16F1 tumor ( 6% ); ( c ) transfection efficiency of electroporation -assisted plasmid DNA delivery was dependent on tumor type; ( d ) integrin -targeted vector, alone or combined with electroporation, was largely ineffective. In conclusion, our results demonstrate that some nonviral methods of gene delivery are feasible and efficient in transfecting solid tumors. Therefore, this makes nonviral methods attractive for further development.
Background: Bleomycin is poorly permeant but potent cytotoxic and radiosensitizing drug. The aim of the study was to evaluate whether a physical drug delivery system -electroporation can increase radiosensitising effect of bleomycin in vitro and in vivo.
Uniform DNA distribution in tumors is a prerequisite step for high transfection efficiency in solid tumors. To improve the transfection efficiency of electrically assisted gene delivery to solid tumors in vivo, we explored how tumor histological properties affected transfection efficiency. In four different tumor types (B16F1, EAT, SA-1 and LPB), proteoglycan and collagen content was morphometrically analyzed, and cell size and cell density were determined in paraffin-embedded tumor sections under a transmission microscope. To demonstrate the influence of the histological properties of solid tumors on electrically assisted gene delivery, the correlation between histological properties and transfection efficiency with regard to the time interval between DNA injection and electroporation was determined. Our data demonstrate that soft tumors with larger spherical cells, low proteoglycan and collagen content, and low cell density are more effectively transfected (B16F1 and EAT) than rigid tumors with high proteoglycan and collagen content, small spindle-shaped cells and high cell density (LPB and SA-1). Furthermore, an optimal time interval for increased transfection exists only in soft tumors, this being in the range of 5-15 min. Therefore, knowledge about the histology of tumors is important in planning electrogene therapy with respect to the time interval between DNA injection and electroporation.
The aim of our study was to evaluate feasibility and therapeutic potential of electrogene therapy with p53 alone or combined with electrochemotherapy using cisplatin on two murine sarcomas with different p53 status. Antitumor effectiveness of three consecutive electrogene treatments with p53 was more effective in wild-type LPB tumors than mutated SA-1 tumors, resulting in 21.4% of tumor cures in LPB tumors and 12.5% in SA-1 tumors. Pretreatment of tumors with electrogene therapy with p53 enhanced chemosensitivity of both tumor models treated by electrochemotherapy with cisplatin. After only one application of this treatment combination in the LPB tumor model, specific tumor growth delay was prolonged in the combined treatment group compared to electrogene therapy with p53 or electrochemotherapy with cisplatin alone, whereas in SA-1 tumors this treatment combination resulted in 31.6% of cured animals. Results of our study show that electrogene therapy with p53 alone or combined with electrochemotherapy is feasible and effective treatment of tumors. The combination of electrogene therapy and electrochemotherapy after only one application resulted in complete regression of tumors.
Electrically-assisted gene delivery is a non-viral gene delivery technique, using application of square wave electric pulses to facilitate uptake of plasmid DNA into the cells. Feasibility and effectiveness of this method in vivo was already demonstrated, elaborating on pulse parameters and plasmid construction. However, there were no studies performed on sequencing and timing of plasmid DNA injection into the tumors and application of electric pulses. For this purpose we measured luciferase expression in two tumor models (LPB fibrosarcoma, B16F1 melanoma) after electrically-assisted gene delivery at varying time intervals between the pCMV-Luc plasmid injection and electroporation. Expression of luciferase was determined by measurement of its activity using luminometer. The results demonstrated that pCMV-Luc plasmid has to be injected before the application of electric pulses, since no measurable expression was detected in the tumors when pCMV-Luc plasmid was injected after electroporation of tumors. In both tumor models the highest transfection efficiency was obtained when pCMV-Luc plasmid was injected not less than 5 minutes but also not more than 30 minutes before the application of electric pulses. The results also demonstrated variability in the transfection efficiency depending on the tumor model. High expression was obtained in B16F1 tumor model (approximately 5500 pg luc/mg tumor) and lower in LPB fibrosarcoma (approximately 200 pg luc/mg tumor). In conclusion, our results demonstrate that regardless of the susceptibility of the tumors to electrically-assisted gene delivery, the best timing for pCMV-Luc plasmid is between 30 to 5 minutes prior to the application of electric pulses to the tumors.
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